The Fell system was the first third-rail system for railways that were too steep to be worked by adhesion on the two running rails alone. It used a raised centre rail between the two running rails to provide extra traction and braking, or braking alone. Trains were propelled by wheels horizontally applied and retracted by springs onto the centre rail, controlled from the cab, as well as by the normal running wheels.[1] In practice, the running wheels could be allowed to run freely to reduce wear, but the centre brake shoes needed to be replaced frequently. For example: the locomotives' shoes were replaced after each journey on the Mont Cenis Pass Railway.[2] Extra brake shoes were fitted to specially designed or adapted Fell locomotives and brake vans, and for traction the prototype locomotive had an auxiliary engine powering the horizontal wheels.[1] The Fell system was developed in the 1860s and was soon superseded by various types of rack railway for new lines, but some Fell systems remained in use into the 1960s. The Snaefell Mountain Railway still uses the Fell system for (emergency) braking, but not for traction.
The Fell system was designed, developed and patented by British engineer John Barraclough Fell. The first test application was alongside the Cromford and High Peak Railway's cable-hauled incline at Whaley Bridge in Derbyshire, England, in 1863 and 1864. The prototype locomotive had separate boilers, regulators and cylinders for the horizontal and vertical drive wheels, but this arrangement was simplified in subsequent versions.[1]
These tests attracted the attention of the French Government, which conducted its own tests on the slopes of Mont Cenis in 1865. As a result, the Mont Cenis Pass Railway was built by a British company as a temporary connection between France and Italy whilst the tunnel under the Alpine pass was being built; shortening the transit time for mail from Britain and France to Italy and beyond.
In 1913 Fell's son George Noble Fell published variations of his father's apparatus using either electric traction or "gaseous fuel". For electric traction the centre rail would also act as the current conductor rail; the horizontal drive wheels would adhere by magnetism, and the brakes would be applied by electromagnets. For the internal combustion version the horizontal guide wheels would be coated with carborundum for improved grip.[3] [4]
The following railways have used the Fell system. Of these, the only one still in operation is the electrified Snaefell Mountain Railway on the Isle of Man, which occasionally uses the centre rail for braking only; the cars are all now equipped with rheostatic braking, which meets all normal braking needs. The only surviving Fell locomotive, New Zealand Railways H 199, is preserved at the Fell Locomotive Museum, Featherston, New Zealand, near the site of the Rimutaka Incline.